Method of separating sylvite from sylvinite ore



June 17, 1958 FINES KCI IN TAILS J. E. LAWVER 2,839,190

METHOD OF SEPARATING SYLVITE FROM SYLVINITE ORE Filed July :50, 1954 I *1 SYLVINITE /a Q 29 WASHING ORE 7 MEDIUM 1/ I (2)2 v Egg 2a GRINDING I WASHING 2/ SOLIDS SLURRY ST M v TO FILTRATION 3 sIzlNG 7 24 A V .25 //7 I V I DRYING FINES N NS R SEPARATION C0 D5 A30 -/.9 H2O 3/ LE GRouND oRI: I 7

STORAGE 2 CHARGNG V KCI IN CONC.

IN V EN TOR.

M KM

ATTURNEX United States Patent C METHGD OF SEPAQATING SYLVITE FROM SYLVINITE ORE James E. Lawyer, Lakewood, Colo., assignor to International Minerals & Chemical Corporation, a corporation of New York Application July 30, 1954, Serial No. 446,837

9 Claims. (Cl. 209-127) The instant invention relates to the separation of sylvite from sylvite-bearing minerals. Still more particularly, it relates to the electrostatic separation of halite and sylvite occurring naturally or produced artificially.

Separation of sylvite from potash ore such as sylvinite ore may be accomplished by a variety of methods. one method, the potassium chloride is extracted with a hot solution saturated with respect to sodium chloride. The solution is flash-cooled to deposit potassium chloride crystals which are then filtered, Washed, and dried. The mother liquor is then recycled.-

In another process, sylvinite ore is pulverized and liotation agents are used to convey potassium chloride away from the sodium chloride or halite. Following flotation, the sylvite is Water-washed to partially leach away residual halite, and dried.

These processes have one or more disadvantages. The process wherein potassium chloride is extracted from hot saturated brine, for example, is expensive, due to the large quantities of potassium chloride remaining uncrystallized and recycled in the mother liquor, and due to the large heat requirements. in the flotation process, processing costs are relatively high because of the nonrecoverability of expensive reagents utilized to selectively coat one of the ore constituents and thereby selectively float the syl vite or halite away from the other nonfloated material with which it is associated in nature.

It is Well known that particles of minerals which can be induced to take electrical charges of opposite sign can be separated from one another by a number of systems whereby electrical equipment sets up repulsive forces for particles having one charge, and attractive forces for particles of opposite charge. In one form of apparatus involving a charged electrical drum, particles having a charge opposite to that of the drum are held by attraction to the surface of thedrurn and thus moved through an arc of a greater number of degrees than particles having the same charge as the drum. The material dropping from the roll or drum thus may be caught in different hoppers or chutes.

Such systems have, however, failed to effect any appreciable separation of dry potassium chloride particles from other dry ingredients found in association with potassium chloride ores. The systems found efiective to induce dry particles of other minerals to accept an appreciable and substantial electrostatic charge have not been eifective in the treatment of potassium chloride particles, because the sylvite particles have not become sufficiently strongly charged with reference to the gangue compounds of the ore to effect a selective electrostatic separation.

It is an object of the present invention to overcome the limitations and disadvantages of the above discussed prior methods.

It is an object of the present invention to provide a relatively inexpensive method of recovering sylvite from sylvite-containing ores.

Patented June 17, 1958 It is a further object to provide an improved and economical process for the beneficiation of sylvinite ore.

It is a further object to provide a beneficiation method wherein the use of costly reagents such as are employed in flotation processes is avoided.

It is still another object to provide a method wherein the dry products are separated and recovered in condition ready for shipment.

It is still another object to provide a method for the recovery of sylvite in which the ore is comminuted and treated so that the sylvite particles will accept a definite charge and then, when selectively charged, the particles are separated by deflection from a straight path when falling free in an electrostatic field.

These and other objects of the invention will become more apparent from the following description in which.

one embodiment of the invention will be set forth in detail.

It has now been discovered that sylvinite ore such as is found in the Carlsbad sectionof New Mexico can be separated into its component parts, i. e., sylvitc can be separated from sodium chloride or halite particles if such particles are properly washed prior to charging, then selectively charged and subjected to the attractive or repulsive forces of an electrostatic field.

The process of the present invention comprises crushing sylvinite ore containing potassium chloride or sylvite to produce a granular liberated product, washing the granular product with a medium in which at least the potassium chloride component, preferably both components, of the ore constituents is substantially insoluble, inducing the washed particles to accept an electric charge, and passing the charged granular material as freely-falling bodies through a zone where the particles deviate from a straight path due to the forces exerted by an electrostatic field, the deflection of the differentially charged particles towards poles of opposite polarity resulting in separation of the chemically dissimilar particles.

In the operation of this process the feed material, generally a raw ore, is crushed sufliciently to unlock its constituents and screened by the usual procedures to produce a granular product having a particle size in the range of approximately 24 mesh and +200 mesh determined by standard screens. Particles in this size range are sufficiently comminuted or disintegrated to separate the ore into individual particles of sylvite on the one hand, and minerals associated therewith, such as halite, on the other hand.

comminuted particles of sylvite-bearing ore, such as sylvinite ore from the Carlsbad section of New Mexico, mixed ore (i. e. potassium magnesium sulfate, potassium chloride and sodium chloride), and like ore material, after sizing are subjected to a washing step. The washing step effects removal of slime material from the surface of the particles. The term slime as used herein includes fine particles having the same chemical composition as one of the principal components of the ore, as well as material chemically different from the principal components of the ore such as montmorillonite type clays. The washing medium is one in which the potassium chlo ride, and preferably both sylvite and halite, is substantially insoluble so that there will be substantially no loss of potash. In addition, the washing medium must have sufiicient volatility to evaporate leaving a clean surface without requiring the application of high temperatures or extremely low pressures. By high temperatures is meant temperatures higher than approximately 300 C. By low pressures is meant a vacuum (subatmospheric pressure) of, for example, at least 25 inches of mercury. These restrictions do not mean that higher temperatures or other vacuum conditions are not usable, but that such octanes, kerosene, benzene, toluene, and the like; halogencontaining derivatives of hydrocarbonsfsuch as di-chlor ethylene,'tri-chlor ethylene, tri-bromo ethylene, di-chloro bromo propylene, and the like; liquid oxygen-containing derivatives of hydrocarbons, e. g., aliphatic alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tertiary butyl alcohol, n-amyl a1cohol, methy1 n-propyl carbine-l, and the like; amino, nitro, and halogen substituted aliphatic alcohols, and the like; liquid unsaturated alcohol such as allyl alcohol cyclic-alcohols such as furfuryl alcohol, diallyl carbinols, and the like. Additional useful Washing media are the ethers such as ethyl ether,propyl ether,

8,,8 dichlor diethyl ether, and the like; mixed ethers such as methylethyl ether,'ethylpropylethen'and the like; esters of organic and inorganicacids such as ethyl'acetate, butyl propionate, secondary and tertiary butylnitrite, ethyl chloride, ethyl bromide n-hexyl chloride, and equivalent compounds; ketones such as acetone, and the like; and compatible mixtures thereof. 7 V

Following. the Washing, it is necessary that the washing medium be removed and the comminuted sylvite be rendered substantially dry. In climates where relative :humidities of they order of or less prevail, the drying of sylvite presents no particular problem inasmuch as the hygroscopic particles cannot pick up suflicient moisture to render the particle surfaces moist. ln climates where humidity is high,.as for, example the relative humidity reaches in the range of 75% to 95%, the air contacting the sylvite must be conditioned to have a low moisture content.

Drying of the particles may be accomplished by heat: ing the washed ore material to a temperature in the range of about 30 C. to about 300 C. For example, propyl alcohol may be evaporated at temperatures in the range of about 30 C. under vacuum and about 100 C. without vacuum, or by blowing hot-air through a comminuted material or by subjecting a relatively thin layer of particles to infrared heatingrays or other equivalent drying methods. Drying of the washed ore particles may be carried outin apparatus such as a tunnel dryer, rotary kiln, fluidized bed dryer, or equivalentapparatus. By the positioning of a condenser in the exhaust or vacuum line, the washing medium may be recovered for reuse. Recovery of this Washing medium material reduces the processing cost,

inasmuch'as approximately 97% to 99% recovery can.

be obtained under good plant operating practice.

After the comminuted material is dried, the particles are induced to accept an electrical charge. As distinguished from other methods in common use wherein, for example, material is not merely polarizedas. in the case ofpyroelectric crystals, the charging of the particles may be and preferably is carried out in theabsence of an electric field. Sylvite particles may be differentially electrified to carry an electrical charge of different character or of diiferent magnitude from the other components of the comminuted mixture. I Differential electrification may be created by utilizing :the contact potentialxphenomenon such as by frictional or'rubbing contact between particles either when in. contact :withga grounded do'norplate or not. When the quantities of difierent ore. components are not widely disproportionate, contact potential charging may be effectively carried out by, agitation or movement of the'mixture; Under such conditions a. donor plate is not critical to the, operation. When charging concentrate,-

particularly. ,of relativelyQhigh purity,.contact potential will give only weak charging of one component of the it is preferred to operate with a total impressed difference in potential of about 70,000 to about 90,000 volt ,--almixture and at this stage use of a donor element is generally advantageous. By grounded donor plate is meant an element of low work function which readily exchanges electrons with the ore'particles when the plate is grounded to the earth and for optimum charging would have a work function between the two components which it is desired to separate. One method of accomplishing charging of the particles is to convey warm .potashmaterials having a temperature in the range of approximately 150 to approximately 350 F. to a feeder designed to create agitated movement of the particles as 'they pass along the feeder. The donor surface of the feeder maybea metallic chute, plate, tray, hopper or similar device, the surface of the fee'der'being a conductorsuch as lead,-zinc, aluminum, copper, tin, and thelike Dielectric or nonconducting materials vary in their ac.-

ceptance of a charge. In general, it may be stated that electrons flow from the material of, lower work function to the material of higher work function, with theresult that the sylvite particles becomencgative'ty charged. The charge on the sylvite particles is at lea ore particles or gangue, the majority of which particles of the remainder are positiveiy charged,

v Charged particles are fed as free-falling bodies be: tween the electrodes of one or more electrostatic sep arating units, i. e.,'in a path normally not in contact with said electrodes. Within each separating unit there is positioned an insulated pair of oppositely charged electrodes, preferably inthe form of plates or cylinders having opposed faces of considerable area.

The strength of the electrostatic. field which willeifec;

approximately to approximately 200 mesh, to 15,000

volts per inch of distance separating electrodesffor separating coarser particles. In all such discussion of field.

strength, it must be borne in mind that corona ,discharges which ionize air are to be avoided. In general,

though voltages as low as about 20,000 volts and :as high as about 200,000 volts are utilized on occasion. This voltage should be maintained at ahighdirect voltage potential substantially free of alternating current components; i. -e., filtered-D. C. current should ,below in the so-called A. C. ripple. A steady supply of vD. .C. voltage may also be obtained without expensive:filter.- ing apparatus by the use of such equipment as radio frequency power supply.

The process for separating ore into its components will be more fully understood from the following description given by'way of example with reference to the separation of sylvite from sylvinite ore given in conjunction with the drawings in which: a

Figure 1 is a diagrammatic flow sheet of the beneficiation process. 7

Figure 2 is a chart showing the beneficiation accomplished' with and without the washing operation.

For a more detailed illustration of the operation ofthe instant process, reference is made to Figure 1. In this flow sheet, sylvinite ore is transferred from a storage station 10 by a conveyor belt 11 to a grinding mill 12.

At mill 12 the sylvinite ore is broken up into a size sub-' size, are removed at separating station ,16 to which'the i 24 mesh material is delivered by a pneumatic conveyor st definitely more negative than the charge. on most of the remainder of the The voltage may vary from 5,000volts,

17 and are discarded. The material of a size in the range of about 24 and about +200 mesh is dropped from separator 16 to a storage or surge bin 18.

Coarse material from surge bin 18 was screened four times to remove fines, heated, charged, and fed to the electrostatic separation apparatus without the wash treatment of the instant invention. The results of this separation are shown in Figure 2. The difference in beneficiation of surge bin ore is clearly shown by comparison densed at 26. The recovered liquid is delivered through pipe 27 to storage station 22, from which it is recirculated to the washing station 20. Washing medium plus dissolved and suspended solids from washing station 20 is cooled as at cooler 28 by circulation of cooling medium to crystallize any dissolved solids such as sodium chloride. Solids slurry is removed from cooler 28 and the solids removed from the associated washing medium as by a conventional filter operation. The solids free washing medium from cooler 28 is delivered to storage station 22 through pipe 29. Washed ore issuing from oven 23 in substantially dry condition is passed by conveyor to a grounded donor element 31 which preferably is in the form of a galvanized iron delivery chute where the particles pick up electrons and become charged.

The ore thus charged is subjected, preferably immediately and before appreciable cooling, to an electrostatic field created by a suitable electrostatic separator 32, preferably of the type where the particles, as free-falling bodies, pass between oppositely charged electrode plates spaced six inchs apart and having a potential gradient of 5,000 to 12,000 volts per inch of distance separating the electrodes.

Upon passing through one electrostatic field, a sylvite concentrate product 33, a middling fraction 34, and a halite fraction are obtained.

Example I A sylvinite ore was comminuted and screened to produce a feed having a particle size in the range of 28 and +100 mesh. The ore was washed with an alcoholic medium consisting of methyl alcohol and ethyl alcohol. The washed ore was dried by placing the ore in an electric oven for approximately one hour. When dry, the warm ore was passed over a grounded, galvanized iron chute and then fell between the plate electrodes having a potential gradient of approximately 12,000 volts per inch.

Results are as follows for one pass between the electrodes:

Percent Percent Percent Wt. K01 NaCl Feed 100. 0 40. s 57. 2 5 K01 product- 32. 4 78.1 20. 4 NaCl fraction. 29. 8 8. 6 87. 4 Middling 37. 8 40. 8 56. 7

Example II A sylvinite ore was comminuted to the same particle size as in Example I. The ore was washed with trichloroethylene using approximately 320 cubic centimeters per grams of ore. The washed ore was dried by placing in an electric oven for approximately one hour. The ore was dried in the same electric oven utilized to dry the washed ore of Example I. The warm ore was charged by passing over a grounded iron chute. From the chute, the washed ore fell between electrodes having a potential gradient of approximately 12,000 volts per inch.

Results are as follows for one pass between the electrodes:

Percent Percent Percent Wt. NaCl Feed 100. 0 24. 0 73. 0 K01 product 32. 5 50. 5 47. 0 NaCl fraction 38. 4 4. 3 91. 0 Mlddling 29. 1 21. 7 75. 0

Figure 2 shows that for one-pass separations, without a washing treatment, the concentration of sylvite in the tail fraction rises rapidly when increasing the sylvite content of the concentrate. On the other hand, when utilizing alcohol washed ore, the sylvite content of the tail fraction increases only slowly until attempts are made to raise the sylvite content of the concentrate above 77%.

This application is a continuation-in-part application of my application Serial No. 199,023, filed December 4, 1950, now forfeited, and entitled, Method of Separating Sylvite from Sylvinite Ore.

Having thus fully described and illustrated the character of the invention, what is desired to be secured and claimed by Letters Patent is:

l. The method of beneficiating potash ores containing sylvite comprising comminuting the ore, Washing the comminuted ore with a substantially nonaqueous, nonresidue forming organic liquid medium in which at least the sylvite component of the ore constituents is substantially insoluble, drying the washed ore, selectively inducing transfer of electrons to the washed particles thereby creating a charge thereon, subjecting the charged ore to the attractive and repulsive forces of a high potential electrostatic field, and recovering a product rich in sylvite content and a product low in sylvite content.

2. The method of beneficiating potash ores containing sylvite comprising comminuting the ore, washing the comminuted ore with a substantially nonaqueous, nonresidue forming organic liquid medium in which at least the sylvite component of the ore constituents is substantially insoluble, heating the washed ore to a temperature in the range between about 60 F. and about 300 F. whereby the Washing medium is evaporated and the ore dried, inducing the hot dried particles to accept an electric charge, subjecting the charged ore to the attractive and repulsive forces of a high potential electrostatic field, and recovering a product rich in sylvite content and a product low in sylvite content.

3. The method of beneficiating potash ores containing sylvite comprising comminuting the ore, washing the ore with a substantially nonaqueous, nonresidue forming organic liquid medium in which at least the sylvite component of the ore constituents is substantially insoluble, drying the washed ore, selectively inducing the transfer of electrons to the washed particles thereby creating a charge thereon, passing charged ore through an electrostatic field having a potential gradient in the range of between about 5,000 volts per inch and 15,000 volts per inch and having a total impressed ditterence in potential of between about 20,000 volts and about 200,000 volts, and recovering a product rich in sylvite content and a product low in sylvite content.

4. The method of beneficiating potash ores containing sylvite comprising comminuting the ore, washing the comrninutedorewith anormally liquid mediurn selected from the group consisting :r-of halogen-containing and oxygen-containing derivatives of hydrocarbons, drying the Washed ore, selectively inducing transfer of electrons to the Washed particles thereby-creating acharge. thereon, subjecting the charged oret'to the attractive and repulsive forces of a high potential electrostatic field, and recovering a product-rich in sylvite content and a product low in sylvite'content.

5.'The method of beneficiating potash ores containing 'sylvitecomprising comminuting theores, washing the comminuted ore with a substantially nonaqueous alcoholic medium, drying the washed ore, selectively inducing transfer ofelectrons to the washed particles thereby creating a charge thereon,.subjecting the charged oreto, the ,attractive and repulsive forces of a high potential electrostatic field, and recovering a product rich in sylvite content and a product low in sylvite content; 7

6. The method'of beneficiating potash ores containing sylvite comprising. comminuting thelore, washing the comminuted, ore withsubstantiallyn anhydrous ethyl alcohol, drying the:washed ore, selectively inducing transfer ing a product rich in sylvite content and'a product low in sylvite content. t

8. The method of beneficiating sylvinite ore comprising comminuting the ore, washing the comminu'ted: ore with a substantially nonaqueous alcoholic medium, heating jccting the'char ed oreto pressures less than-atmospheric,

condensing the-released; vapors to recoverealcohol for the washe'dpre to a'temperature in the range of hetween" about- 6 0 B and about 300- :Fwand simultaneously sub- ,iecting the washedore'to pressures lessthan atmospheric, 7 c'ondensihgthe released-vapors to recover alcohol for recirculation in I the washing' system, selectively inducing transfer of electrons to thedry: washed particle s, subjecti ing charged ore to; the attractive and repulsive forces ofa high potential electrostatic field, and recovering a mod I 'uct rich in {sylvitecont'ent and a product low in s'ylvite content. I

- 9. Thernethod'of heneficiatingpotash ores comprising oornminuting the ore, washing-the vcomrninuted ore with a; substantially n'onaqueous alcoholic I medium, heating the washed orefto ax'ternperature in the range of between about 60 and about 300 1P1, and simultaneouslysub recirculation l in the] washing system, inducing transfer of "electrons to thef-dry washed particles, passing the charged ore as fre'ely falling bodies between the -'electrodes of a high potential electrostatic 'field, collecting a sylvite-rich portion and a s'ylvite-lean portion and at least" one portion of-sylvite contained intermediate therebetween, and recycling theintermediate portion wherebyaf sylvite-rich portion -:is recovered for addition to said sylvite-rich product.

V Referen c esffiited in thefile of this patent UNITED STATES- PATENTS 2,168,681 Obrien Aug. 8, v1939 2,197,865 Johnson; Apr. 23, 1940 2,236,445 r Pfeilfer Mar. .25, 1941 2,556,483 'Peery; June12, 1951 2,593,431 Fraas Apr. 22,

' OTHER REFERENCES Bureau'of Mines, R; I. 3 667, Contact PotentialiIn Electrostatic SeparationF'November1942, pages 7-12. 

1. THE METHOD OF BENEFICIATING POTASH ORES CONTAINING SYLVITE COMPRISING COMMINUTING THE ORE, WASHING THE COMMINUTED ORE WITH A SUBSTANTIALLY NONAQUEOUS, NONRESIDUE FORMING ORGANIC LIQUID MEDIUM IN WHICH AT LEAST THE SYLVITE COMPONENT OF THE ORE CONSTITUENTS IS SUBSTANTIALLY INSOLUBLE, DRYING THE WASHED ORE, SELECTIVELY INDUCING TRANSFER OF ELECTRONS TO THE WASHED PARTICLES THEREBY CREATING A CHARGE THEREON, SUBJECTING THE CHARGED ORE TO THE ATTRACTIVE AND REPULSIVE FORCES OF A HIGH POTENTIAL ELECTROSTATIC FIELD, AND RECOVERING A PRODUCT RICH IN SYLVITE CONTENT AND A PRODUCT LOW IN SYLVITE CONTENT. 